Multi-element fuel cell system

Abstract

A multi-element fuel cell system comprises a substantially cylindrical former (2), a rechargeable hydrogen fuel source (3) and a plurality of fuel cell elements (4). The former comprises a series of interconnecting modules each perforated to allow passage of fuel to the fuel cell elements. Each fuel cell element (4) is positioned radially outwardly of the former (2) and is provided with channels, arranged to receive and direct fuel gas, an anode current collector, a gasket (12), a first diffusion backing layer (8), a membrane electrode assembly (10), a second diffusion backing layer (9) and a cathode current collector (11). The cathode current collector applies even compression to the fuel cell element, such that good electrical contact is maintained within each fuel cell element. The fuel cell elements are electrically connect in series via respective anode and cathode current collectors and then capped at each end of the former for connection to equipment. The former and current collectors have substantially the same coefficient of thermal expansion and the fuel source is coupled to the fuel cell elements. The system is suitable for man-portable applications.

What is claimed is:  
     
       1. A multi-element fuel cell system, the system comprising a substantially cylindrical former; a rechargeable hydrogen fuel source; and a plurality of fuel cell elements; wherein the former comprises a series of interconnecting modules; wherein each former module is perforated to allow passage of fuel to the fuel cell elements; wherein each fuel cell element is positioned radially outwardly of the former, each element being provided with channels, arranged to receive and direct fuel gas, an anode current collector, a gasket, a first diffusion backing layer, a membrane electrode assembly, a second diffusion backing layer and a cathode current collector; wherein the cathode current collector comprises a perforated area and tabs at end designed to interleave; wherein the cathode current collector applies even compression to the fuel cell element, such that electrical contact is maintained within each fuel cell element; wherein the fuel cell elements are electrically connected in series via respective anode and cathode current collectors; wherein the fuel cell elements at each end of the former are capped for connection to equipment; wherein the former and current collectors have substantially the same coefficient of thermal expansion; and wherein the fuel source is coupled to the fuel cell elements. 
     
     
       2. A multi-element fuel cell according to  claim 1 , wherein the former acts as the anode current collector. 
     
     
       3. A multi-element fuel cell system according to  claim 1  the system further comprising an outer porous, hydrophobic layer, such that rate of loss of water from the membrane electrode assembly during operation is optimised. 
     
     
       4. A multi-element fuel cell system according to  claim 3 , wherein the outer layer is chosen from one of perforated cellulose wrapping, expanded polystyrene and polyimide foam. 
     
     
       5. A multi-element fuel cell system according to  claim 1 , wherein the hydrogen fuel source comprises one of a hydrogen store or a hydrogen generator. 
     
     
       6. A multi-element fuel cell system according to  claim 1 , wherein the hydrogen source comprises a metal hydride of up to 2 wt % H 2 , a primary hydride, compressed hydrogen or hydrogen stored in carbon nanofibres. 
     
     
       7. A multi-element fuel cell system according to  claim 1 , wherein the hydrogen source is provided in a replaceable cartridge. 
     
     
       8. A multi-element fuel cell system according to  claim 1 , wherein the membrane electrode assembly comprises a catalyst of platinum deposited on a carbon support. 
     
     
       9. A multi-element fuel cell system according to  claim 8 , wherein the catalyst comprises between 0.2 and 1.0 mg of platinum per cm 2 . 
     
     
       10. A multi-element fuel cell system according to  claim 1 , wherein the cathode current collector and the former comprise stainless steel. 
     
     
       11. A multi-element fuel cell system according  claim 1 , wherein the tabs of the cathode current collector are fastened in place by spot welding. 
     
     
       12. A multi-element fuel cell according to  claim 1 , wherein a fine wire mesh is provided in contact with the interior surface of the cathode current collector. 
     
     
       13. A multi-element fuel cell system according to any preceding  claim 1 , further comprising an impervious outer shell and means for ensuring air flow to the fuel cell elements beneath the outer shell. 
     
     
       14. A method of manufacturing a multi-element fuel cell system, the method comprising laying down a cathode current collector, a first diffusion backing layer, a membrane electrode assembly, and a second diffusion backing layer to form a stack; wherein the cathode current collector comprises a perforated area with tabs at each end, folding the stack around a former; interleaving the cathode current collector tabs; applying a predetermined pressure to the cathode current collector to ensure contact between the stack and the former; fastening the cathode current collector in place to form a fuel cell element; and connecting a plurality of fuel cell elements together to form a fuel cell. 
     
     
       15. A method according to  claim 14 ; wherein the tabs of the cathode current collector are fastened in place by spot welding. 
     
     
       16. A method according to  claim 14 ; wherein the cathode current collector is formed by photo-fabrication. 
     
     
       17. A method according to  claim 14 , further comprising capping the ends of a fuel cell for connection to equipment; and coupling the fuel cell to a fuel source. 
     
     
       18. A method according to any of  claim 14 , further comprising applying a porous, hydrophobic layer over the cathode current collector, such that rate of loss of water from the system is optimised.